We purchased a new TV a couple of months ago and needed to modify the existing mount. The first thing we realized was that our new TV had 100mm x 100mm holes and our old TV had larger bolts and they were spread out quite a bit further.
To get the TV in and working (the old one died), we drilled the 100mm x 100mm holes (a few times as it is difficult to get them lined up right) and bolted the TV to the existing mount after cutting off one of the wings so that the cables could be connected. This worked for over a thousand miles, but we were concerned that over time we might have a problem. Also, trying to get 4 holes lined up, level and plumb wasn't so easy - the TV slanted to the left and wasn't square with the existing opening.
While kicking back with a cocktail I suggested that Kat bend some steel and make a mount that wouldn't require precision attachment to the existing mount. Are you confused at this point? I am!
Kat bent some steel to make a shelf that sits on the wooden drawer front and bolts to the existing mount. I asked her to use some heavy stock so that it could easily support the TV.
Once it was screwed to the door front and bolted to the existing mount we checked to make sure the vents for the TV weren't blocked (she let me cut out for the vents - that's why they don't look so hot).
Here's where it gets cool. She took a piece of steel, drilled the requisite M4 100mm x 100mm holes and then drilled a 5/8" hole in the middle. The idea is that after drilling a hole in the existing mount, the entire front, including drawer front can be tweaked left or right to make everything square with the cabinetry by turning clockwise or counter-clockwise.
Here's the end result. I'm happy again, because I can watch TV with a cocktail in hand and I don't have to worry about the TV falling.